1. Field of the Invention
This invention relates to the separation and recovery of a concentrated acid from an aqueous solution and more particularly, to the separation and recovery of concentrated hydrochloric acid from the crude product obtained from the acid hydrolysis of cellulose.
2. Description of the Prior Art
Wood and other lignocellulosic materials have long been known as a source of various sugars, such as glucose, useful in the food and chemical industry. These sugars can be produced by the acid hydrolysis and saccharification of wood or other plant material containing cellulose in solid, divided form. Strong mineral acids, such as concentrated (greater than about 20 weight percent) hydrochloric acid, are throught to be the preferred acids for the hydrolysis of cellulose as noted by H. F. J. Wenzl, The Chemical Technology of Wood, Academic Press (New York, 1970).
Hydrolysis with concentrated acid of a lignocellulosic material produces a crude product comprising concentrated acid and the various sugars obtained from the hydrolysis of cellulose. For such processes to be commercially feasible, the concentrated acid must be economically separated and recovered, preferably then recycled to the hydrolysis reaction. Present separation and recovery technology is essentially evaporation, such as that described in Swiss Pat. No. 609,092. There the crude product is dried by direct contact with a stream of hot gas, such as air, to produce a powdery mixture comprising the sugars formed by hydrolysis. The sugars are then recovered from the powdery mixture by contacting the mixture with water. While this method is operable, it is undesirable because it it both energy and capital intensive. Moreover, the high temperatures associated with this method of recovery promote thermal degradation of the hydrolysate sugars and thus the recovered sugars may contain significant amounts of reversion sugars, i.e., oligomers of glucose, xylose, etc.
Use of solvent extraction to separate and recover concentrated acid and simultaneously concentrate the sugars from the crude product would be desirable because it is less energy and capital intensive than evaporation technology. Moreover, if such a recovery method could be operated at relatively ambient temperatures, then the formation of reversion sugars would not be promoted (at least to the extent of the evaporation method). However, the present art does not offer solvent extraction technology useful for this particular separation and recovery. For example, Crittenden et al., "Extraction of Hydrogen Chloride from Aqueous Solutions", Ind. and Eng. Chem., 265 (February 1954) teach the use of various aliphatic alcohols for the recovery of dilute hydrochloric acid from aqueous streams but contains no discussion with regard to the separation and recovery of concentrated hydrochloric acid from mixtures containing the acid in combination with hydrolysis sugars.
Mrnka et al., "Extraction of Monobasic Acids by Amines", Proc. Int. Sol. Ext. Conf., Vol. 1, (1974), teach the use of various amines for the extraction of monobasic acids from aqueous solutions.
Blumberg et al., "Interesting Aspects in the Development of a Novel Solvent Extraction Process for Producing Sodium Bicarbonate", Proc. Int. Sol. Ext. Conf., Vol. 3, 2789 (1974), also teach the use of amines for extracting hydrochloric acid from an aqueous solution.
Duhayon et al., U.S. Pat. No. 4,036,939, teach the recovery of hydrogen chloride in gaseous form from an organic solvent loaded with hydrochloric acid in a dilute aqueous solution by dehydrating the loaded organic solvent in a dehydration extractor in which the solvent is circulated countercurrent to an aqueous solution having a high chloride concentration. The organic solvent loaded with dilute hydrochloric acid is selected from the group of aliphatic alcohols having preferably a relatively high molecular weight, such as 2-methylbutanol-4.
Kreevoy et al., U.S. Pat. No. 3,186,809, teach the use of dodecylphenol as a synergistic additive in the amine extraction of inorganic mineral acids from aqueous solutions.